To Summon the Dead is a spell written in the WarrenBook of Shadows. This ritual summons the dead from the afterlife, bringing them into the physical world in the form of a spirit. When they step out of the circle of candles, the spirit will corporealize.

After the death of Prue Halliwell, Piper deperately tried to summon this sister and bring her back. However, her Grams appeared instead. Piper later used the spell again asking her Grams to explain what she meant when she said the Charmed Ones' destiny still awaited. After saving Paige, they used the same spell to summon Patty to let Paige meet her birth mother.[1]

Penny Halliwell explained that Piper could not summon Prue until she was ready. Piper first needed to move on with her life and follow her new destiny[6].

Spirits cannot always be summoned, at least not with this spell. Piper once tried to summon Grams and mentioned that it did not work. However, her unborn child was able to summon her without use of the spell[7].